This invention relates to vehicle retarder systems and more particularly said systems having both hydraulic and friction brake retardation.
Vehicle retardation systems which employ the vehicle service brakes and the hydraulic retarder in concert have been utilized in the past. These operating systems generally use the service brake only when the rapid retardation is required to bring the vehicle to a stop. During normal retardation, only the hydraulic retarder is in use since continued slipping of the vehicle service brakes causes significant heat generation and brake wear. It has also been proposed to control the transmission drive ratio during retardation. In these systems, the transmission is shifted to a lower drive ratio so the torque converter is driven at a high speed to maximize the engine braking; and an input driven retarder is also driven at a very high speed to improve the braking efficiency of the retarder.